Percentages Study Guide: GED Math

Converting Decimals to Percents

Changing decimals to percents is the opposite of what you've just done. When you change a decimal to a percent, you move the decimal point two digits to the right.

Examples

1. Convert 0.15 to a percent.

Move the decimal point two places to the right: 0.15 becomes 15.

Add a percent sign after the number: 15%.

Therefore, 0.15 = 15%.

2. Convert 7.9 to a percent.

Move the decimal point two places to the right.

Add zeros as needed: 7.9 becomes 790.

Add a percent sign after the number: 790%.

Therefore, 7.9 = 790%.

Converting Percents to Fractions

To change a percent to a fraction, you write the percent over 100. Don't forget to reduce the fraction to lowest terms as you would any other fraction. Here are the steps to follow.

Step 1   Drop the percent sign.

Step 2   Write the number as a numerator over 100.

Step 3   Write improper fractions as mixed numbers.

    Reduce the fraction to lowest terms.

Examples

1. Convert 15% to a fraction.

Drop the percent sign: 15% becomes 15.

Write the number as a numerator over 100: .

Reduce the fraction to lowest terms. Both 15 and 100 can be divided by 5: .

Therefore, 15% = .

2. Convert 150% to a fraction.

Drop the percent sign: 150% becomes 150.

Write the number as a numerator over 100: .

Write the improper fraction as a mixed number, and reduce the fraction to lowest terms: .

Therefore, 150% = 1.

Converting Fractions to Percents

There are two basic ways to convert fractions to percents. You should try both ways, and see which one works better for you.

Method 1

Step 1   Divide the numerator by the denominator.

Step 2   Multiply by 100. (This is the same as moving the decimal point two digits to the right.)

Step 3   Add a percent sign.

Method 2

Step 1   Multiply the fraction by .

Step 2   Write the product as either a whole or a mixed number.

Step 3   Add a percent sign.

Example

Change to a percent.

Method 1

Divide the numerator by the denominator.

Multiply by 100: 0.4 × 100 = 40.

Add a percent sign: 40%.

Method 2

Multiply the fraction by .

Write the product as either a whole number or a mixed number: 40.

Add a percent sign: 40%.

Although you can always convert between percents, decimals, and fractions using the described methods, it's a good idea to know common percent, decimal, and fraction equivalents for standardized tests. Knowing them in advance can save you valuable time on a timed test. Besides, working with a value in one form is often easier than working with it in another form. Knowing the equivalents can help you see the easier route faster. Here are some common equivalents you might want to learn.

Practice problems for these concepts can be found at:

Percentages Practice Problems: GED Math